R data.table-带有':='的新列并保留现有列 [英] R data.table - new column with ':=' and keep existing column

问题描述

是否可以创建一个新列，并在语句中保留(很少)现有列?例如创建"x"列，然后保留"x"和"mpg"列

Is it possible to create a new column and keep (few) existing columns in the statement ? e.g. creation of "x" column and then keeping "x" and "mpg" column

dt <- data.table(mtcars)

dt[,x:=mpg]

dt[,.(x,mpg)]

推荐答案

如果您要使用:= 进行引用替换，则可以

If you want to do the replacement by reference, using := then you can do

dt[, x:=mpg][, setdiff(colnames(dt), c('x', 'mpg')) := NULL]

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